Induction electric furnace



2 Shuts-Sheet 1 H. ILBERG I'NDUCTIQN ELECTRIC FURNACE Filed Oct.- 10.1933 d a 5.0 6 8 d Oct. 16, 1934;

Heinz Ilberg, Berlimfiiiarlottenburg, German Application October 10,

In Germany August 1, 1932 Claims. (CI. 13-29) The majority of the knowninduction furnaces,

'in which the melting channels, which form the secondary winding of atransformer, are of relatively small cross-sectional area and terminate6 in a crucible serving as melting pool or bath, make use either ofpinch-effect, motor efiect, repulsion effect and buoyancy due to heat,or of a combination of these electrodynamic and thermic effects of theelectric current.

10 The melting channels are also constructed accordingly. A commonfeature 'ofall these furnaces is, that a heat accumulation takes placeat a certain point in the melting channel. This point can be locatedfrom consideration of the symmetrical construction of the furnace, or isknown from experience, because the ceramic lining of the furnaces isgenerally broken through by the molten metal at this point.

It is obvious. that the flow caused by the buoyancy due to heat,hereinafter briefly referred to as heat flow, begins at this point andis preferably directed in one direction and is superimposed on themovements in the melting channel caused by the electrodynamic forces.

According to the invention the heat accumulation and therefore the heatflow are influenced to a considerable extent and their detrimentaleffects avoided, which effects consist in a local or partial overheatingof the material and in a strong eating away of the ceramic lining of thefurnace which must result in the furnace being quickly rendered unfitfor service.

Two embodiments of the invention are illustrated in the accompanyingdrawings in which:

Fig. 1 is a longitudinal section through one form of construction of aninduction furnace.

Fig. 2 is a similar view of another form of construction.

Fig. 3 is a side elevation of a somewhat variant form of furnace fromthat shown in Figs. 1 and 2.

Fig. 4 is an end elevation of the furnace of Fig. 3, the view being fromthe end indicated by the arrow A.

A secondary winding 0, which serves as a melting channel surrounds aprimary coil 0. with iron core b and terminates in a melting bath d.

Owing to the electrodynamic forces a strong flow is produced in themelting channel a which is directed uniformly outwards and inwards onboth channel arms. The strength of the flow is dependent upon the squareof the current strength divided by the cross section. The course of flowis indicated in Fig. 1. It can be seen, that the flow at e has areversing zone so that the material to be melted can only be moved from1933, Serial No. 692,923'

this zone with dimculty. Moreover, o frictional resistances the speed ofthe-eleg y namic flow decreases considerably with thelength of the path,so that the greatest speed existence,

the channel mouths f and g and the slowesaat -dflrg the point e. As aresult of this the displacement of the molten material from the point eis checked, so that the molten material is at this point subjected for arelatively long time to the heating effect of the electric current andis 06 strongly overheated. As is known, the melting channels ofinduction furnaces are based on a certain nominal cross sectionaccording to the service conditions to be fulfilled. One might endeavorto overcome the above mentioned drawbacks by increasing theconstructional nominal cross section of the melting channel. This,however, is open to the objection that, on the one hand the efficiencyfactor of the furnace is detrimentally affected and on the other handthe drawing effect of the electrodynamic flow is reduced. It isdiflicult to estimate whether, owing to the reduced frictionalresistances, the electrodynamic flow still extends to the same point asin the case of smaller cross .sectional area or not. If it does notextend so far, nothing is attained by enlarging the cross sectionalarea; on the contrary, a greater heat buoyancy effect, that is again agreater overheating, is necessary to shift the material from the pointe.

In order to overcome the above mentioned difficulties, it is proposed,according to the invention, to enlarge the cross sectional area of themelting channels along a portion of their length or along their entirelength above the nominal cross sectional area of one of the channel arms.and to again reduce same to the nominal cross sectional area of theother channel arm. The point, at which the heat accumulation takesplace, is situated in the above example (Fig. 1) at the point of themelting channel, which is equidistant from the two channel mouths. Theenlargement is designated by h in Fig. 1. It preferably merges graduallyinto the original cross section. The proportion of the length of thewidened portion of the melting channel to the total length of thechannel depends upon the actual working conditions, the material to bemelted and the form of construction of the melting channel. It isevident that two limits are possible which, however, are of practicalimportance. In one instance the cross section is only widened in directproximity to the point of greatest heat accumulation and in anotherinstance, starting from the mouth of the melting channel,

the cross section of the melting channel is gradually widened to thepoint where the greatest heat accumulation takes place. The channelcross sectional area will be widest at this point and again graduallyreduces towards the other mouth of the melting channel. The latterconstruction is illustrated in Fig. 2, the individual parts correspondto those shown in Fig. 1 and are consequently designated by similarreference characters.

In the case of furnaces, which utilize the repulsion effect of theprimary coil (Figs. 3 .and 4), the melting channel 0 is very often madeof hellcal shape or crossed in order to obtain a uni-directional flow inthe melting channels. In order to attain this, the repulsion effectought to be made very strong, so that it overcomes the inwardly andoutwardly directed flow (see'Fig. 1) caused by the pinch-effect. .Astrong repulsion effect of the coil results, however, in a bad outputcoeiilcient. Therefore, one has hitherto generally been satisfied with alower repulsion effect, which causes a one-sided flow, that issuperimposed on the outwardly and inwardly directed flow. Consequently,the point where a heat accumulation takes place is displaced towards theside of the channel arm onwhich the outwardly directed flow caused bythe pinch-- effect" and the flow caused by the repulsion eifectcounteract each other. The widening h of the channel cross section musttherefore be arranged at the same point. This point is no longersituated. as mentioned above, equidistant from the 1 two channel mouthsbut shifted towards one of the channel mouths. The reference charactersotherwise correspond to those of Figs. 1 or 2.

The invention has been described in connection with twoforms of example.According to the construction of the melting channel and to the objectto be attained it can also be employed in another form of construction.It can likewise be employed appropriately when, for example, the mouthsof the melting channel have different cross sectional areas, forinstance 9 and ,1 according to Fig. 3 and Fig. 4. Particularly it isimmaterial what relative position the melting channels occupy withrespect to the melting bath, whether they are vertical, horizontal orinclined, and what cross sectional shape they have.

I claim:-

1. An induction smelting furnace, comprising melting channels which formthe secondary winding of a transformer, the cross sectional -area of themelting channels being widened upon the whole length of the channelcommencing from the nominal cross sectional area of the one channel armand again narrowing to the nominal cross sectional area of the otherchannel arm.

2. An induction electric furnace of the type having a pool for moltenmetal and walls forming a single submerged channel which forms thesecondary of a transformer, in which the cross-' sectional area of thechannel is widened intermediate between the extremities of the channelat the point where excessive heating would otherwise develop.

3. An electric induction furnace of the type having a pool for moltenmetal and walls forming a submerged channel which forms the secondary ofa transformer, in which the cross sectional area of the channel isprogressively and gradually widened and then progressively and Ygradually narrowed from a point near one extremity toa point near theother extremity of the channel, the widened and narrowed portions havingprogressively curved contours.

4. An electric induction furnace of the type having a pool for moltenmetal and walls forming a singledepending submerged channel below thepool, in which the channel is of horseshoe contour and is continuouslyand progressively enlarged in cross section from points on either sideof the middle point toward the middle point, the enlarged portion havinga progressively curved contour.

5. An electric induction furnace of the type having a pool for moltenmetal and walls forming a single submerged channel, which increases incross section from one end to the other, in communication with the pool,in which the channel cross section on the side of the channel nearestthe largest end of the channel and at the point at which the channeltends to overheat is enlarged with respect to the immediately adjoiningchannel cross sections.

HEINZ ILBERG.

